1. Field of the Invention
This invention relates to plow blades for snow plows, earth working devices, and the like, and more particularly to a plow blade having carbide inserts along the bottom forward edge of the plow blade for improved impact and wear resistance.
2. Background
Graders and snowplows are both well known and each has a relatively long moldboard which extends generally laterally of the surface being worked and is moved over the surface in a direction generally perpendicular to the length of the moldboard. Such support members are typically concave on the forward side and adapted for mounting beneath or in front of a power device, such as a truck or tractor. Such plows also typically include a detachable blade which may be attached, typically by bolting, to the lower edge of the support member so as to project downwardly from the support member. Such blades normally withstand most of the impact and abrasive wear to which the plow blade is subjected and as a result are typically made from a quality grade of steel. A lower edge of the blade forms the working surface of the blade.
Grader blades made of steel have the advantage of being relatively inexpensive, but also the disadvantage of wearing out extremely rapidly. Because blade edges are subjected to abrasive wear and impact damage, the wear rate can be extremely high at times. When a blade edge wears down beyond a predetermined point, it must be replaced with another blade edge. The replacement of blade edges is, of course, time consuming, represents down time for the equipment, and requires the maintenance of a replacement parts inventory. If a worn blade edge is not replaced, wear at the lower edge of the blade edge would continue until the support member suffers damage by exposure to the surface being worked on.
Thus, over the years, various techniques, such as impregnation and hardfacing of the blade cutting edge with carbide particles, and attachment of cemented carbide inserts into or onto the blade edge have been employed in attempting to prolong the life of the steel blade.
Blades with cemented carbide inserts, generally referred to as buttons in the industry, have a compact cylindrical shape. These compact inserts are disclosed in U.S. Pat. No. 5,813,474, for instance. The compact insert in FIG. 4 of U.S. Pat. No. 5,813,474 is at one end generally semispherical and at the other end has a blunt stepped section 46. The semispherical section is more resistant to impact damage. In FIG. 2 of '474, a drilled hole in the steel blade body 24 with a compact insert 16 brazed therein is illustrated. As is shown at 38 in U.S. Pat. No. 5,813,474, the bottom of the drilled bore was drilled out by a standard drill bit and is conical. Braze material is placed into the drilled out bores and, next, the compact button is inserted into the bore and then the blade is heated, forming a braze between the compact button and the steel body. The bore does not cooperate with the compact insert like-a-glove, as seen in FIG. 2 of '474. At the bottom of the bore a generally conical space remains after insertion of the compact insert. This remaining conical space is filled with braze material. In this prior art design after the brazing process is complete, voids are much more likely to be present in this conical space in comparison to tight fitting members. Efforts at solving this problem in the industry have included manufacturing the bores with an end mill that forms a cylindrical bore having a flat circular bottom and have been successful in forming a tighter fit between the compact inserts and bores. Although successful in preventing the propensity of voids in the connecting braze, cutting out the bore with an endmill is a much more expensive and more time consuming machining operation in comparison to drilling out the bores with a standard drill.
The use of protruding lane marker reflectors on highways has grown significantly in popularity over recent years. These lane markers are typically attached to the road surface and extend slightly above the road surface. While these reflectors greatly improve lane visibility, they present a problem when the road must be plowed. When typical prior art carbide block/bar inserts within prior art blade edges impact the reflector lane markers, the carbide block/bar inserts, which are more susceptible to impact damage than steel, are sometimes damaged. Furthermore, because such prior art carbide block inserts are typically brazed adjacent to each other, carbide inserts adjacent to the damaged insert are susceptible to crack propagation damage. The same type of damage may also occur when such typical prior art carbide block inserts strike irregularities in the road surface, such as potholes or ruts.
In prior art blades, uniform cemented tungsten carbide bar inserts have been employed on blades to reduce and limit damage to the steel blades. Such blades are disclosed in the sales brochure “Kennametal snowplow blades and accessories” (1995), published by Kennametal Inc., AM95-17(5)F5. The cemented tungsten carbide bars are aligned side by side across the width of the blade. Steel blade edges having cemented wear resistant hard metal carbide block/bar inserts distributed along the lower edge of the blade edge have been employed in an attempt to prolong the life of the blade edge. Other examples of such block/bar inserts are disclosed in U.S. patents to Stephenson et al. (U.S. Pat. No. 3,934,654) and Stephenson (U.S. Pat. No. 3,529,677). The tungsten carbide bars/blocks brazed onto the steel body are positioned side-by-side across the width of the blade and are brazed to each other at their sides. A cemented tungsten carbide bar on these prior art blade designs would sometimes fracture/crack on account of an unusually large impact force. The crack in a cemented tungsten carbide bar of the prior art often was not limited to just a single bar, but would propagate into bars adjacent thereto along large portions of the width of the blade.
Generally speaking, the use of the two sets of tiered cemented tungsten carbide inserts in the bottom edge of a grader blade is known, for instance, in U.S. Pat. No. 4,770,253, to Hallissy et al. The blade in the front recess in Hallissy is made from tungsten carbide having a high cobalt content, 18%-22% cobalt by weight, so as to adapt it for impact wear resistance during use of the grader blade. The intermediate slot contains a second insert composed of cemented tungsten carbide containing 10% to 13% weight percent cobalt. The inserts are brazed to the steel blade body including the intermediate and rear sections thereof. However, in contrast to the construction of the grader blade of the present invention, the prior art Hallissy grader blade has tiered inserts and does not have an independent intermediate slot spaced from the front recess, with the inserts respectively disposed in the recess and the slot. In the present invention the front recess is formed along the forward bottom edge of the blade, whereas the intermediate slot is formed along and opens toward the bottom edge of the blade and is separated from the front recess of the steel blade body. In Hallissy '253 and other prior art, the cemented tungsten carbide bars are brazed together in side-by-side relation. These brazed together tungsten carbide bars function to form a unitary piece of cemented tungsten carbide that spans the width of the blade. If one of the cemented tungsten carbide inserts fractured due to an excessive impact force, a crack would propagate into adjacent carbide inserts across the connecting braze joints.
In the above discussed tiered insert designs, as shown in U.S. Pat. No. 4,770,253, the rearline row of insert bars is brazed into a recess in the steel blade and the frontline of insert bars is brazed onto the rearline row of inserts. The brazing together of the frontline and rearline inserts results in an inherent disadvantage in tiered insert designs. Whenever a front line insert is pried off, for instance by contact with an obstruction on the road whenever the vehicle is placed in reverse, the adjoining rear line insert typically is knocked off together with the front line insert. Not only is the loss of two insert bars of tungsten carbide expensive, the less wear resistant steel portion of the blade becomes exposed.
The use of the two lines of hard material spaced apart from each other along the bottom edge of a grader blade is also known in the prior art, Kengard A grader blade made and sold by Kennametal, see sales brochure “Kengard A grader blades,” Kennametal Inc., Latrobe, Pa., publication B84-19(5)A4;B83-145 (1983) discloses spaced hard material inserts. This prior art Kengard A grader blade has a front recess, and an intermediate slot spaced from the front recess, with the inserts respectively disposed in the recess and the slot. The front recess is formed along the forward bottom edge of the blade, whereas the intermediate slot is formed along and opens toward the bottom edge of the blade. The slot is defined between and spaced from the front recess and a rear surface of the blade by intermediate and rear bottom end sections of the steel blade body. The front recess contains a first insert composed of Kengard A material, a metal composite of tungsten carbide particles in a matrix of tough, work-hardening stainless steel. The intermediate slot contains a second line of inserts composed of cemented tungsten carbide containing 10 to 13 weight percent cobalt. The inserts are brazed to the steel blade body. However, the prior art Kengard A grade blade of such construction frequently experienced binder washout between the carbide particles in the composite metal matrix, braze failure due the inherent porosity of the matrix, and overall was not cost effective. The grader blade construction of the present invention eliminates these problems.
While many of these prior art blades would appear to operate reasonably well under the limited range of operating conditions for which they were designed, most seem to embody one or more shortcomings in terms of complexity, performance, reliability and cost effectiveness which make them less than an optimum design. Consequently, a need exists for a different approach to grader blade design, one which will more adequately address the kinds of wear and forces encountered by the lower end of the grader blade.